1. Field of the Invention
The present invention relates to thin-film magnetic heads provided with magnetoresistive thin-film elements in which the resistance changes greatly in response to changes in external magnetic fields, and more particularly, to a technique using a structure in which a longitudinal bias magnetic field is satisfactorily applied to a free magnetic layer.
2. Description of the Related Art
A giant magnetoresistive (GMR) head utilizing an element having a giant magnetoresistive effect (GMR effect) has been known as a magnetoresistive read head for reading magnetic data from a magnetic recording medium such as a hard disk. A spin-valve type head has been known as a GMR head having a relatively simple structure and a high rate of resistance change in relation to an external magnetic field.
FIG. 20 is a sectional view of an example of a structure of such a spin-valve type GMR thin-film element.
The structure shown in FIG. 20 includes a laminate 207, that is trapezoidal in section, in which an underlying layer 201, a free magnetic layer 202, a nonmagnetic conductive layer 203, a pinned magnetic layer 204, an antiferromagnetic layer 205, and a protective layer 206 are deposited on a substrate in that order. Hard bias layers 208 and conductive layers 209 are formed so as to cover the inclined sides of the laminate 207.
In the structure shown in FIG. 20, the pinned magnetic layer 204 has a higher coercive force than that of the free magnetic layer 202, and the pinned magnetic layer 204 is aligned in a single-domain state in the Y direction in FIG. 20 by an exchange anisotropic magnetic field caused by the antiferromagnetic layer 205 deposited directly on the pinned magnetic layer 204, and the magnetization direction is fixed in the Y direction.
The hard bias layers 208 are magnetized in the X1 direction in FIG. 20, and since the free magnetic layer 202 adjacent to the hard bias layers 208 is aligned in a single-domain state in the X1 direction by the hard bias layers 208, Barkhausen noise, which is generated by the formation of many magnetic domains in the free magnetic layer 202, is prevented from occurring.
In this structure, a sensing current is applied from the conductive layer 209 to the free magnetic layer 202, the nonmagnetic conductive layer 203, and the pinned magnetic layer 204. The driving direction of a magnetic recording medium such as a hard disk is set in the Z direction in FIG. 20, and when a fringing magnetic field from the recording medium is applied in the Y direction, the magnetization of the free magnetic layer 202 changes from the X1 direction to the Y direction. Because of the relationship between the change in the magnetization direction in the free magnetic layer 202 and the fixed magnetization direction of the pinned magnetic layer 204, the electrical resistance changes, and the fringing magnetic field from the recording medium is detected by a voltage change based on the change in the electrical resistance.
FIG. 21 shows an example of another structure of a spin-valve type element, in which a bias is applied in a manner different from that in the structure shown in FIG. 20. The structure shown in FIG. 21 includes a laminate 217 in which an underlying layer 211 composed of Ta, a free magnetic layer 212 composed of an NiFe alloy, a nonmagnetic conductive layer 213 composed of Cu, a pinned magnetic layer 214 composed of an NiFe alloy, an antiferromagnetic layer 215 composed of an FeMn alloy, and a protective layer 216 composed of an insulating material are deposited on a substrate 210 in that order. On both sides of the laminate 217, ferromagnetic layers 218 composed of an NiFe alloy, antiferromagnetic layers 219 composed of an NiMn alloy, and conductive layers 220 composed of Cu are deposited.
In the structure shown in FIG. 21, the pinned magnetic layer 214 is aligned in a single-domain state in the direction represented by an arrow 222 (in the Y direction) by an exchange anisotropic magnetic field caused by the antiferromagnetic layer 215 deposited on the pinned magnetic layer 214, and the magnetization direction is fixed in the Y direction. The antiferromagnetic layer 219 composed of the NiMn alloy is not antiferromagnetic at room temperature. However, when heated, the antiferromagnetic layer 219 becomes antiferromagnetic, and by applying a magnetic field in the direction represented by an arrow 221 (in the X1 direction) in FIG. 21 during heat treatment, the magnetization is aligned along the direction of the applied magnetic field. After the heat treatment, the magnetization of the antiferromagnetic layer 219 is fixed, generating an antiferromagnetic coupling with the ferromagnetic layer 218, and the free magnetic layer 212 can be aligned in a single-domain state in the magnetization direction of the ferromagnetic layer 218 also in the structure shown in FIG. 21. Thus, the magnetoresistive effect can be obtained without causing Barkhausen noise.
With respect to the structure shown in FIG. 20, in which the free magnetic layer 202 is aligned in a single-domain state by the hard bias layers 208, ends of the free magnetic layer 202 tend to become insensitive zones in which the magnetization direction does not easily change under the influence of the magnetization direction of the hard bias layers 208, resulting in a hindrance to the narrowing of tracks associated with the improvement in the recording density of magnetic recording media.
Therefore, in view of the narrowing of tracks, the biasing method shown in FIG. 21, in which no hard bias layer is used, could be effective. However, the application of a bias in the structure shown in FIG. 21 gives rise to the following problems.
In the structure shown in FIG. 21, the antiferromagnetic layer 215 pins the magnetization direction of the pinned magnetic layer 214, and the antiferromagnetic layer 219 aligns the free magnetic layer 212 in a single-domain state for biasing. The magnetization directions caused by the antiferromagnetic layer 215 and the antiferromagnetic layer 219 differ by 90xc2x0.
Although the magnetization directions of the antiferromagnetic layers 215 and 219 are usually controlled by deposition in a magnetic field or magnetic annealing after deposition, it is very difficult to align the magnetization of the antiferromagnetic layer 219, which is formed later, in a direction different from that of the magnetization of the antiferromagnetic layer 215, which is formed first, without disturbing the magnetization direction of the antiferromagnetic layer 215.
As described in the specification of Japanese Unexamined Patent Publication No. 8-45032 (Japanese Patent Application No. 7-122104) which discloses the structure shown in FIG. 21, the aforementioned problem can be avoided by a method in which, using a magnetic film of an FeMn alloy and a magnetic film of an NiMn alloy having different Nxc3xa9el temperatures, the magnetic film having a higher Nxc3xa9el temperature is firstly subjected to high-temperature heat treatment for aligning the magnetic field, and secondly the magnetic film having a lower Nxc3xa9el temperature is subjected to low-temperature heat treatment for aligning the magnetic field in the direction different from that in the first heat treatment by 90xc2x0. However, since the FeMn alloy constituting an antiferromagnetic layer has a low Nxc3xa9el temperature and has a low blocking temperature at which antiferromagnetism is believed to disappear, a bias magnetic field caused by the antiferromagnetic layer made of the FeMn alloy easily becomes unstable due to heat generated when a magnetic recording device such as a hard disk drive is operated.
Furthermore, in the structure disclosed in Japanese Unexamined Patent Publication No. 8-45032, an NiMn alloy film having a high Nxc3xa9el temperature which requires heat treatment is used for applying a longitudinal bias, and an FeMn alloy film having a low Nxc3xa9el temperature is used for pinning the magnetization of a pinned magnetic layer. However, since the NiMn alloy film for applying the longitudinal bias is usually deposited after an antiferromagnetic layer and the pinned magnetic layer are deposited, the heat treatment of the NiMn alloy film is performed subsequently to the deposition or the heat treatment of the antiferromagnetic layer and the pinned magnetic layer, and thus the characteristics of the spin-valve film comprising the antiferromagnetic layer and the pinned magnetic layer may be adversely affected by the heat treatment of the NiMn alloy film.
Accordingly, it is an object of the present invention to provide a thin-film magnetic head provided with a magnetoresistive thin-film element in which a structure for applying a longitudinal bias magnetic field to align a free magnetic layer in a single-domain state is employed, the longitudinal bias magnetic field can be applied satisfactorily, the structure is easy to fabricate, and stable characteristics are obtainable, as well as to provide a method of producing the same.
In accordance with the present invention, a thin-film magnetic head provided with a magnetoresistive thin-film element, as an element for reading magnetic data, includes a laminate including an antiferromagnetic layer, a pinned magnetic layer formed in contact with the antiferromagnetic layer, the magnetization direction of the pinned magnetic layer being fixed in a predetermined direction by an exchange coupling magnetic field caused by the antiferromagnetic layer, and a free magnetic layer formed on the pinned magnetic layer with a nonmagnetic conductive layer therebetween, the magnetization of the free magnetic layer being aligned in the direction perpendicular to the magnetization direction of the pinned magnetic layer. Soft magnetic layer is formed at both sides of the laminate. Secondary antiferromagnetic layer formed in contact with the soft magnetic layers for generating a unidirectional exchange coupling in the soft magnetic layers and applying a bias magnetic field to the free magnetic layer, and conductive layers are formed. The antiferromagnetic layer generates a unidirectional exchange coupling by heat treatment to fix the magnetization of the pinned magnetic layer, and the secondary antiferromagnetic layers generate the unidirectional exchange coupling as deposited without heat treatment.
In accordance with the present invention, the magnetoresistive thin-film element may have a dual-type structure in which the nonmagnetic conductive layer, the pinned magnetic layer, and the antiferromagnetic layer are formed on each side of the free magnetic layer in the depth direction.
In accordance with the present invention, at least one of the pinned magnetic layer and the free magnetic layer may be separated into two layers by a nonmagnetic layer, in which the magnetization directions of the separated layers differ by 180xc2x0, resulting in a ferrimagnetic state.
In accordance with the present invention, the antiferromagnetic layer may generate the unidirectional exchange coupling because a disordered structure is transformed into an ordered structure by heat treatment after deposition.
In accordance with the present invention, the antiferromagnetic layer may be composed of one of an Xxe2x80x94Mn alloy and a Ptxe2x80x94Mnxe2x80x94Xxe2x80x2 alloy, where X is an element selected from the group consisting of Pt, Pd, Ir, Rh, and Ru, and Xxe2x80x2 is at least one element selected from the group consisting of Pd, Ir, Rh, Ru, Au, Ag, Cr, and Ni.
In accordance with the present invention, the secondary antiferromagnetic layer may be composed of an Xxe2x80x3xe2x80x94Mn alloy, where Xxe2x80x3 is at least one element selected from the group consisting of Ru, Rh, Ir, Pd, and Pt.
In accordance with the present invention, an underlying layer composed of a nonmagnetic conductor may be formed between the laminate and the soft magnetic layers.
In accordance with the present invention, a method of producing a thin-film magnetic head provided with a magnetoresistive thin-film element includes the steps of forming a laminate including an antiferromagnetic layer having a disordered structure, a pinned magnetic layer, a nonmagnetic conductive layer, and a free magnetic layer; performing heat treatment on the antiferromagnetic layer to transform the disordered structure into an ordered structure so that the magnetization of the pinned magnetic layer is fixed in a predetermined direction by an exchange coupling magnetic field by the antiferromagnetic layer; and forming soft magnetic layers, secondary antiferromagnetic layers, and conductive layers at both sides of the laminate so that the magnetization of the free magnetic layer is aligned in the direction perpendicular to the magnetization direction of the pinned magnetic layer by a unidirectional exchange coupling of the secondary antiferromagnetic layers through the soft magnetic layers.
In accordance with the production method of the present invention, when the heat treatment is performed, a magnetic field is preferably applied in the height direction (in the direction of the height of the element).
In accordance with the production method of the present invention, heat treatment is preferably performed on the secondary antiferromagnetic layer at a temperature that is lower than the blocking temperature of the secondary antiferromagnetic layer so that the structure of the secondary antiferromagnetic layer is not transformed.
In accordance with the production method of the present invention, the secondary antiferromagnetic layer is preferably deposited while applying a magnetic field in the track width direction.
In accordance with the production method of the present invention, heat treatment may be performed on the secondary antiferromagnetic layer at a temperature that is lower than the blocking temperature of the antiferromagnetic layer and higher than the blocking temperature of the secondary antiferromagnetic layer so that the structure of the secondary antiferromagnetic layer is not transformed.